1. Field of the Invention
This invention relates to a water-containing binder composition based on polyisocyanates and mixtures of at least two different water-dispersible or water-soluble polyol components polymers, to a process for the production of these binder compositions and to their use as binders for coating and sealing compositions.
2. Description of the Prior Art
Ecological factors play an important part in coatings technology. A particularly important problem is to reduce the quantities of organic solvents used in coating compositions.
In the case of chemically crosslinking polyurethane lacquers, which are particularly important in the coating field by virtue of their outstanding properties, it has not been possible until very recently to eliminate the use of organic solvents. The use of water instead of organic solvents in two-component polyurethane coating compositions based on polyisocyanates containing free isocyanate groups did not appear possible for some considerable time because isocyanate groups are known to react not only with alcoholic hydroxyl groups, but also with water. In addition, the concentration of active hydrogen atoms from water in these systems is far higher than the concentration of hydroxyl groups from the organic NCO-reactive component. Accordingly, it must be assumed that the isocyanate/water reaction with formation of urea and carbon dioxide takes place in the ternary polyisocyanate/organic polyhydroxyl compound/water system. This isocyanate/water reaction is detrimental because it does not result in crosslinking of the organic polyhydroxyl compounds and also causes foaming of the mixture through the formation of carbon dioxide.
It was only recently recognized (DE-OS 3,829,587) that selected polyhydroxy polyacrylates could be combined with polyisocyanates containing free isocyanate groups to form water-based two-component systems. These coating compositions have a pot life of several hours and cure to form high-quality crosslinked films which are comparable in their properties to coatings previously obtained from solvent-containing two-component polyurethane coating compositions.
It has now been found that certain mixtures of water-containing polymer polyols based on at least two different polyester- and/or polymer-based polymers and polyisocyanates containing free isocyanate groups can also be used as binders. These binders have long pot lives, excellent flow during film formation and good pigment wettability.